As is well known, stencils are widely used in the application of markings to shipping containers. In many cases, it is desired to apply the same markings to shipping documents and it is economical to create the stencil and the marked shipping documents through the same marking operation, generally by the striking of typewriter keys.
Stencil-forming sheets are generally made by impregnating a porous, ink-pervious, fibrous tissue base sheet with an ink-impervious material so that the sheet becomes ink-impervious except in the localized areas where the sheet is struck by a typewriter or printer key or by printer pins.
Typically, the stencil impregnant has a pastel color, against which a typed or printed message, such as a shipping address, can be read easily if it is typed or printed in black ink, as by an inked ribbon between such keys or pins and the surface of the stencil-forming sheet.
When it is desired, to simultaneously type or print the same message onto an underlying sheet, such as a top sheet of a tabbed set of business forms, it has been necessary to have a separate "carbon" coating on the underside of the stencil sheet, the side opposite that which is struck by the keys or pins.
A separate "carbon" coating requires a separate coating operation with a coating composition different from the composition of the ink-impervious impregnant and thus adds both material and handling costs to the cost of the stencil-forming sheet.